Riboflavin-responsive oxidative phosphorylation complex I deficiency caused by defective ACAD9: new function for an old gene

Mike Gerards, Bianca J C van den Bosch, Katharina Danhauser, Valérie Serre, Michel van Weeghel, Ronald J A Wanders, Gerry A F Nicolaes, Wim Sluiter, Kees Schoonderwoerd, Hans R Scholte, Holger Prokisch, Agnès Rötig, Irenaeus F M de Coo, Hubert J M Smeets

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Abstract

Mitochondrial complex I deficiency is the most common oxidative phosphorylation defect. Mutations have been detected in mitochondrial and nuclear genes, but the genetics of many patients remain unresolved and new genes are probably involved. In a consanguineous family, patients presented easy fatigability, exercise intolerance and lactic acidosis in blood from early childhood. In muscle, subsarcolemmal mitochondrial proliferation and a severe complex I deficiency were observed. Exercise intolerance and complex I activity was improved by a supplement of riboflavin at high dosage. Homozygosity mapping revealed a candidate region on chromosome three containing six mitochondria-related genes. Four genes were screened for mutations and a homozygous substitution was identified in ACAD9 (c.1594 C>T), changing the highly conserved arginine-532 into tryptophan. This mutation was absent in 188 ethnically matched controls. Protein modelling suggested a functional effect due to the loss of a stabilizing hydrogen bond in an α-helix and a local flexibility change. To test whether the ACAD9 mutation caused the complex I deficiency, we transduced fibroblasts of patients with wild-type and mutant ACAD9. Wild-type, but not mutant, ACAD9 restored complex I activity. An unrelated patient with the same phenotype was compound heterozygous for c.380 G>A and c.1405 C>T, changing arginine-127 into glutamine and arginine-469 into tryptophan, respectively. These amino acids were highly conserved and the substitutions were not present in controls, making them very probably pathogenic. Our data support a new function for ACAD9 in complex I function, making this gene an important new candidate for patients with complex I deficiency, which could be improved by riboflavin treatment.

Original languageEnglish
Pages (from-to)210-219
Number of pages10
JournalBrain
Volume134
Issue numberPt 1
DOIs
Publication statusPublished - Jan 2011

Keywords

  • Acyl-CoA Dehydrogenases
  • Electron Transport Complex I
  • Exercise
  • Genotype
  • Homozygote
  • Humans
  • Mitochondria
  • Mitochondrial Diseases
  • Mutation
  • Pedigree
  • Phenotype
  • Riboflavin

Cite this

Gerards, M., van den Bosch, B. J. C., Danhauser, K., Serre, V., van Weeghel, M., Wanders, R. J. A., Nicolaes, G. A. F., Sluiter, W., Schoonderwoerd, K., Scholte, H. R., Prokisch, H., Rötig, A., de Coo, I. F. M., & Smeets, H. J. M. (2011). Riboflavin-responsive oxidative phosphorylation complex I deficiency caused by defective ACAD9: new function for an old gene. Brain, 134(Pt 1), 210-219. https://doi.org/10.1093/brain/awq273